1. Field of the Invention
This invention relates generally to the field of microwave transmission and more particularly to a microwave buffer for placement between transmitter modules and an impedance combiner for protecting the remaining circuitry from the destructive effects of a reflected signal caused by a disconnected port.
2. Description of the Prior Art
The solid state transmission of microwave signals is known that utilizes transmitter modules. The power from each transmitter module is combined to form a single, more powerful signal which is transmitted through the antenna. Generally, this is done by running the signals from the transmitter modules through an impedance combiner. When all of the transmitter modules are operating and are connected to a matched load, there are essentially no reflected waves. However, when the voltage from the modules looks into a variable load or a short circuit, the reflected voltage at certain phase angles can add up unevenly and detrimentally to very high voltages if one of the transmitter modules is disconnected. Standing waves develop when the system is unmatched. The standing waves can direct toward any module. If that occurs, the circuitry of that module could be severely damaged. When transmitting signals, it is ideal to transmit in one mode, namely, the in-phase mode. However, when the impedance combiner is larger than a half wavelength and driven unequally more than one mode will be created. Thus, waves are allowed to bounce around inside the system in a resonant fashion known as ringing. When a transmitter module is disconnected, mutual coupling imbalances add together vectorally to produce a standing wave of amplitude and phase error. These waves would then launch themselves back into the feed system (because the undriven port is not loaded) and towards the output port causing the output to oscillate with frequency.
Thus, in microwave transmission systems that utilize combiners of modular transmitters, a means is needed for preventing damage to the circuitry of remaining modules when one is no longer inputting power. This means should also tend to keep the output as in-phase and as low loss as possible, accounting only for the loss of the module disconnected.